My invention relates to an improved method of and apparatus for calcining limestone and, more particularly, to a more efficient method of and apparatus for removing lime dust from air that has been used to cool hot lime produced in the calcining process.
As is known in the prior art, limestone, which is largely calcium carbonate, is reduced to lime or calcium oxide by subjecting the limestone to a high heat for a predetermined period of time. The resulting lime has a wide variety of uses. For example, it is used in the production of steel.
Limestone is heated to very high temperatures of over 1600.degree. F. in the calcining process. When lime is removed from the hearth at such high temperatures it is beneficial to remove much of the heat from it so that it may be more safely and conveniently moved and stored and so that its heat may be fed back into the calcining process, thus reducing fuel costs and thermal pollution.
In the prior art, as shown and described in U.S. Pat. No. 3,345,052, issued to Hubert L. Hall, hot lime which has been removed from a calcining hearth passes down a chute into a cooling chamber. A conduit connects the cooling chamber to external dust separators. A fan pulls cool air into the cooling chamber, where it is heated by contact with the hot lime and then through an external conduit to the external dust separators. Then the fan feeds the resultant heated and cleaned air into ducts leading to the burners used to provide heat for the calcining process.
One problem with the arrangement described above is that an excess of heat is lost by the use of an external duct between the cooling chamber and the dust separators and by the use of external dust separators themselves. Another inefficiency in the use of external dust separators is that lime dust is deposited in the external conduit leading from the cooling chamber to the external dust separators as well as at the site of the external dust separators themselves. It would be desirable if all this lime dust could be deposited under the cooling chamber where the rest of the lime is collected.